Hard disk drive devices write data or the like to a recording medium using an actuator arm with a head provided to the tip of the actuator arm. The recording medium has data areas to store user data and servo areas to store data used for positioning control of the head.
In such a hard disk drive device, when the head passes over a servo area, the position of the head is determined based on a signal read out from the servo area. The arm adjusts the head position based on the position determined. Thus, the head can be controlled to be located at a desired position.
There are several types of patterns recorded in the servo areas including, for example, null servo patterns, area servo patterns, and phase servo patterns.
For example, a null servo pattern is provided with two blocks of different magnetization patterns. By a positional information signal read out from the two blocks, the position of the head can be determined. Because the null servo pattern only needs two blocks, less servo areas are required, and therefore, data areas are easily secured. There has been disclosed conventional technology related to such the null servo pattern.
In such the hard disk drive device, upon determining the position of the head based on positional information read out from a pattern in the servo area, it is difficult to accurately determine the position of the head using only the conventional technology. This is because it is difficult to associate a read signal with the position of the head with a smooth correspondence relation due to specifications, operational circumstances, and the like of the hard disk drive device. This applies not only to demodulation of a position using a null servo pattern, but also to demodulation using other servo patterns. Therefore, in the hard disk drive device, the read signal needs to be corrected to accurately determine the position of the head.